In known communication systems, such as systems based on orthogonal frequency division multiple access (OFDMA), a common frequency band is shared among many user terminals. The user terminals often monitor the shared channel resources of the system in order to transmit and receive data efficiently. The user terminals receive signaling information related to allocation of the user terminals to specific resources of the common frequency band for transmission and/or reception. An Allocation Table or a corresponding control channel (e.g. a shared control channel) is used to describe the allocation of user data both in downlink and uplink. The Allocation Table can be sent once per a short period of time, i.e. a subframe of transmission time interval (TTI), for example. This is important in order to control packet-switched traffic and the scheduling thereof efficiently.
In a known system, the Allocation Table is transmitted as one self-decodable block for all user terminals. As the block is transmitted over the whole bandwidth, it benefits from the available frequency diversity. However, such a block should be coded and modulated taking into account the lowest signal to interference-plus-noise ratio (SINR) requirements. The performance in such a case is not satisfactory at low SINR and it also consumes radio resources excessively due to a large Information Block length and a low channel-coding rate.
Some methods have been proposed for improving the performance of control channel reception. First, instead of one decodable block the user terminals can be divided into several groups according to their reported SINR. Then, a modulation and coding rate of such blocks can be adjusted respectively. The Allocation Table for user terminals in difficult signal conditions can be coded with low code rate and low order modulation. Further, the transmitted power of the blocks can be differentiated such that higher power is allocated to user terminals having low SINR for improving the reliability in that area. The blocks can be allocated not only as chunk of consecutive sub-carriers but also in a distributed (scattered) manner so that all separately decodable blocks also benefit from frequency diversity. Further, as an alternative, the shared control channel may be arranged as a set of self-decodable information blocks, each of which is intended for a user terminal separately. This kind of shared channel has roughly the same properties as the Allocation Table described above but with a receiver-specific power control (power boosting/power suppression), code rate selection and smaller Information Block Length. Also in this case, the code blocks are distributed (scattered) over a frequency to benefit from frequency diversity.
Receiving of the Allocation Table (i.e. the allocation information) is important because if a user terminal does not succeed in that, it cannot receive any data either. The probability of receiving the Allocation Table should be good in order to guarantee good capacity of the particular radio link. The reception should also work well with a low SINR. Especially at low SINR values, it is difficult to achieve reliable reception of allocation information.